Sealing ring for non-hermetic fluid seals

ABSTRACT

A sealing ring is provided for non-hermetic fluid seals with a restricted passage between sealing elements rotating relative to one another the sealing has a carrier and at least one sealing rib extending radially on the outside or inside around the carrier. The edge of each rib forms a flow restriction with an opposing running in surface, with the sealing rib presenting an abrasive geometry. Each sealing rib has for the most part a smooth, rotationally symmetrical contour, and one or a few cutting elements are arranged at one or a few points on each sealing rib so that each element projects radially and axially on one or both sides from the sealing rib contour.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of German Patent Document 199 33445.5 filed in Germany on Jul. 16, 1999 and PCT/DE00/02309 filed inGermany on Jul. 14, 2000.

The invention relates to a sealing ring for non-hermetic fluid sealswith a restricted passage between coaxial sealing elements rotatingrelative to one another especially as a rotating sealing element forlabyrinth seals in gas turbine engines, with a carrier leading to atleast one component and with at least one sealing rib extending radiallyoutwards or inwards and around the entire carrier, the exposed,circumferential edge of which rib in operation forms a flow restrictionwith a running-in surface situated radially opposite, the sealing ribpresenting an abrasive geometry to the running-in surface.

Thus German Patent Document DE 4341 216 C2 protects a seal component forcontrolled-gap or labyrinth seals having a coating composed of acompound containing metal and hard material particles, the latter beingarranged in the form of regularly shaped bodies with leveled surfaceslying on the same level. This construction is intended to ensure thatthe running-in surface material is not only removed by abrasion butdisplaced by hot plastic flow. This presupposes a large amount of heatgenerated by friction, which can in turn damage the fin material.

Numerous measures are known, which are intended to remedy this problemand come under the term “fin tip armouring”.

Thus DE 4341 216 C2 protects a seal component for controlled-gap orlabyrinth seals having a coating composed of a compound containing metaland hard material particles, the latter being arranged in the form ofregularly shaped bodies with levelled surfaces lying on the same level.This construction is intended to ensure that the running-in surfacematerial is not only removed by abrasion but displaced by hot plasticflow. This presupposes a large amount of heat generated by friction,which can in turn damage the fin material.

German Patent Document DE 197 30 008 C1 protects armouring for a metalengine component, which is worked into a running-in surface as this isskimmed, comprises a ceramic layer and is profiled with peaks andintervening spaces for the discharge of abraded material, the profilingbeing created by deforming of the surface of the component prior tocoating, preferably by knurling. The entire sealing fin is thereforeconstructed like a saw blade with a plurality of teeth uniformlydistributed over its periphery, the surfaces of which teeth areceramic-coated. This solution has the disadvantage, among others, thatthe many spaces between the teeth/tips generally impair the sealingeffect. Owing to the small material cross sections in the tips and thepunctual introduction of heat, local heat flux densities occur here,which may be higher than in the case of smooth sealing fins and hencevery detrimental to the material grain structure. In addition, theV-shaped spaces having sharp edges at the foot form stress-increasingnotches from which dangerous cracks can originate. A coarser toothingwould be advantageous with a view to effective abrasion and hence athermally non-critical running-in process. This is inconsistent with theneed for a good sealing effect, so that in fact only a very fine, flattoothing can be used. In this respect, this solution also tends toresult in a wear process with the thermal disadvantages already referredto.

This object is achieved by the sealing ring for non-hermetic fluid sealswith a restricted passage between coaxial sealing elements rotatingrelative to one another, especially as a rotating sealing element forlabyrinth seals in gas turbine engines, with a carrier leading to atleast one component and with at least one sealing rib extending radiallyoutwards or inwards and around the entire carrier, the exposed,circumferential edge of which rib in operation forms a flow restrictionwith a running-in surface situated radially opposite, the sealing ribpresenting an abrasive geometry to the running-in surface, characterizedin that the/each sealing rib has a smooth, rotationally symmetricalcontour over the greater part of its periphery, and in that one or a fewcutting elements are arranged at one or a few points on the/each sealingrib in such a way that each cutting element projects radially andaxially on one or both sides from the contour of the sealing rib. asuitable , mechanically abradable running-in surface.

This object is achieved by the features characterized in claim 1, inconjunction with the generic features of its pre-characterizing clause.

The sealing ring according to the invention advantageously combines thefeatures of a conventional design with at least one smooth, rotationallysymmetrical sealing rib, and an abrasive design, one or a few cuttingelements, which project from the sealing rib contour, being arranged atonly one or a few discrete points on the sealing rib. The cuttingelements are intended to be of a really cutting or chip-forming designand robust, that is mechanically resistant, so that sufficient surfacematerial is abraded in the shortest possible time and without muchfriction work, thereby producing the desired clearance with the smooth,sealing contour of the sealing rib.

BRIEF DESCRIPTION OF THE DRAWINGS

A chip-forming machining process is known, which is referred to as“thread whirling” and which uses a hollow tool with one or a fewinwardly projecting teeth rotating at high speed, in order to machine aslowly rotating work-piece. Although the tool and the work-piece are notguided co-axially with one another in thread whirling, this processnevertheless gives some idea of the running-in process involved in asealing ring according to the invention.

Preferred configurations of the invention are characterized in thesubclaims.

The invention will now be explained in more detail with reference to thedrawings. These show a simplified representation, not to scale, of thefollowing:

FIG. 1 a coaxial partial section through a sealing ring and a running-insurface interacting with the sealing ring,

FIG. 2 a perspective partial view of a sealing ring with sealingelements of various types.

DETAILED DESCRIPTION OF THE DRAWINGS

The sealing ring 1 according to FIG. 1 comprises an at least largelyrotationally symmetrical carrier 3, which is fixed to at least oneadjoining, rotating component (not shown). Two sealing ribs 5,6 pointingradially outwards, which have a smooth, rotationally symmetrical contourover the greater part of their periphery, are arranged on the carrier 3.The exposed edges 8,9 of the ribs are therefore also largely smooth androtationally symmetrical, that is to say circular cylindrical. It shouldbe added that just one sealing rib or more than two sealing ribs may bearranged on one carrier, that the exposed edges of at least two sealingribs may be graduated in diameter, that is different in size, and thatall or some of the sealing ribs may also project radially inwards fromthe carrier.

The dashed contours 11, 12 indicate cutting elements and theirrotational orbits. It will be seen that the cutting elements 11, 12 eachproject radially and axially on both sides over the sealing ribcontours. This ensures that the sealing ribs 5,6 themselves, includingtheir exposed sealing edges 8,9, virtually never come into contact withthe opposing running-in surface 17, so that measures such as surfacehardening, armouring etc. can as a rule be dispensed with.

As is common in practice, the running-in surface 17 represented bydashed lines as an adjoining, static sealing element is designed as ametal honeycomb structure, the material of which should be abradablewith relatively few problems by machining, i.e. it should exhibit acertain ductility and defined fracturing properties.

Inside areas of the running-in surface 17 are abraded by relative radialand axial movements between sealing ring 1 and running-in surface 17 inexcess of the initial radial clearance, so that after a full-load cycle,e.g. after one flight with manoeuvring, a characteristic running-incontour 18 is formed, which scarcely varies any more, if at all infurther operation. The running-in contour 18 largely corresponds to anexternal envelope curve over all relative, maximum displacements of thecutting elements 11,12 that have occurred.

Since the running-in process constitutes only a small part of thecomponent service life, it is possible on completion to remove thecutting elements or to machine them off flush with the sealing ribcontour. Removable cutting elements may be replaced by replacement partsflush with the ribs. All of this would be feasible, for example, as partof a first engine overhaul.

FIG. 2 shows in detail various designs of cutting elements 13 to 16 on asealing ring 2 with a radially outer sealing rib 7 on a carrier 4, theexposed, sealing edge 10 pointing upwards. A plate-shaped cuttingelement 13, which is arranged axially/radially, that is transversely tothe sealing rib 7 and passing through the latter, can be seen on theleft of the figure. It will be seen that the cutting element 13 projectsradially (upwards) and axially on both sides (front right and rear left)from the sealing rib contour. The cutting geometry is not shown indetail, it being here left to the person skilled in the art to providesuitable angles, chip deflection and chip breaker facilities. Thecutting element 13 will as a rule be composed of a harder material thanthe sealing rib 7, preferably of hard metal, ceramic or a compositematerial based on these. A material bonding connection by soldering oradhesive bonding, for example, to supplement the positive interlock isadvisable, depending on the material. A relief bore 19 can also be seen,which is intended to prevent dangerous notch stresses in the sealing ribmaterial at the foot of the cutting element 13. For sealing reasons therelief bore 19 may be sealed, for example with a plug, with adhesive orsolder. The second cutting element 14 from the left is also ofplate-shaped design, but it is arranged radially and essentiallycircumferentially on one side of the sealing rib 7 in a pocket-likedepression. The unilateral arrangement requires that at least one pairof such cutting elements 14 be arranged per sealing rib, these possiblylying axially opposite one another or being offset in a circumferentialdirection.

The third cutting element 15 from the left differs from the firstcutting element 13 in having a wedge shape, the axial/radial arrangementbeing the same. The wedge shape leads to a positive interlock fixingalso in a radial direction, thereby providing a reliable safeguardagainst centrifugal forces. Additional bonded fixing is howevereffective in preventing axial migration. The wedge shape furthermorecauses a “drawing” cut of the two lateral cutting edges. There may beeffective stress-relief geometries in the area of the two lower wedgecorners passing through the sealing rib 7, but they are not shown here.A special feature of the right-hand cutting element 16 is the purelypositive interlock fixing. For this purpose it has circular cylindricalstepping in the foot area and is of rectangular design in the cuttingedge/head area. It is installed by inserting radially into the sealingring 2 from inside. Safeguards to prevent falling out inside may befitted (not shown). A cutting element of this type admittedly has thedisadvantage that locally it greatly reduces the supporting componentcross section, so that the dimensions of the sealing ring carrier mustbe increased.

What is claimed is:
 1. A sealing ring for non-hermetic fluid seals, thesealing ring comprising: at least one circular sealing rib having anexposed smooth sealing surface over a greater part of an outer peripheryof the sealing rib, the sealing surface in operation forming a flowrestriction with a running-in surface situated radially opposite to thesealing surface; and at least one cutting element arranged on the outerperiphery of the sealing rib, the at least one cutting elementprojecting radially and axially from the exposed smooth sealing surfaceof the sealing rib, wherein the at least one cutting element is composedof one of hard metal, ceramic-coated metal or ceramic and is connectedto the sealing rib by at least one of a positive interlocking and bondedconnection.
 2. The sealing ring according to claim 1, wherein the atleast one cutting element includes a plurality of cutting elementsarranged at diametrical points on the sealing surface of the sealingrib.
 3. The sealing ring according to claim 1, wherein the at least onecutting element is connected to the sealing rib by a bonded connection.4. The sealing ring according to claim 3, wherein the bonded connectionis a soldered connection.
 5. The sealing ring according to claim 3,wherein the bonded connection is an adhesive connection.
 6. The sealingring according to claim 2, wherein the at least one sealing ribcomprises a hard metal.
 7. The sealing ring according to claim 3,wherein the at least one sealing rib comprises a hard metal.
 8. Thesealing ring according to claim 4, wherein the at least one sealing ribcomprises a hard metal.
 9. The sealing ring according to claim 2,wherein each sealing rib comprises a ceramic-coated metal.
 10. Thesealing ring according to claim 3, wherein each sealing rib comprises aceramic-coated metal.
 11. The sealing ring according to claim 10,wherein the bonded connection is an adhesive connection.
 12. The sealingring according to claim 2, wherein each sealing rib comprise s a ceramicmaterial.
 13. The sealing ring according to claim 3, wherein the atleast one sealing rib comprises a ceramic material.
 14. The sealing ringaccording to claim 13, wherein the bonded connection is an adhesiveconnection.
 15. A method of making a sealing ring for non-hermetic fluidseals, the method comprising: providing at least one circular sealingrib with an exposed smooth sealing surface over a greater part of anouter periphery of the sealing rib, the sealing surface forming a flowrestriction with a running-in surface situated radially opposite to thesealing surface; and attaching at least one cutting element to the outerperiphery of the sealing rib, the at least one cutting elementprojecting radially and axially from the exposed smooth sealing surfaceof the sealing rib, wherein the at least one cutting element is composedof one of hard metal, ceramic-coated metal or ceramic and is connectedto the sealing rib by at least one of a positive interlocking and bondedconnection.